So how much pollution are SUVs really pumping out? Is it the 6x figure which seems absolutely incredible? Which kinds of pollution are most important and how do SUVs stack up with those?

One thing I read a while back that I thought was interesting. California has been adding "clean fuel" additives for years now. MTBE reduces the air pollution, at the expense of poisoning the ground water. The other additive, ethanol, increases the evaporation rate of gasoline, thus adding to the number of pollutants in the air.

-Biscuits